Research of fatigue failure of marine auxiliary machine parts and structures in case of various stresses

The article presents the description of construction and substantiation of the fatigue failure model, combining such stages as the formation and growth of cracks in the ship structures parts with different stress concentrators. Submitted for consideration the fatigue damage model includes a sample for research of multi- and low cycle fatigue of damaged material, as well as the condition determining the initial size of the microcrack and characterizing the transition from the first stage of the fatigue damage to the subsequent one. The results of studies of the fatigue damage development and microcrack formation have been shown. The development of fatigue damage accumulation depends on the boundary conditions for the local volume and, consequently, will be controlled by the stresses and strains at some distance from the top of the concentrator. The increase in parameter value with increasing thickness of the sample and the increase in the number of cycles leading to failure is due to the transition of stress-strain state in subsurface layers of the sample from the flat stress state to plane strain state. Comparison between the calculated values of stress concentration effective coefficient and experimental data reported in the literature, shows a sufficiently good agreement for steels of different classes